In a previous study, NCT00582127, two age-matched cohorts, one clinically diagnosed with mild Alzheimer's disease and the other healthy controls, were tested with a hand-held EEG/ERP system to determine if the cohorts could be discriminated using the EEG/ERP measures. This study proposes to retest the AD cohort 18-60 months after their first test to characterize the change in EEG/ERP measures correlated with the longitudinal change in neuropsychological testing.